The aim of the proposed research is to determine the molecular mechanisms by which a cluster of developmentally and hormonally regulated Drosophila genes are controlled. The genes are the structural genes for three salivary gland secretion proteins, sgs-3, sgs-7 and sgs-8. These genes are in the 68C polytene chromosome puff, on the left arm of the third chromosome. Several parallel series of experiments will be performed. One set will concentrate on the mechanisms by which two known trans-acting factors, the steroid hormone ecdysterone and the product of the X-chromosomeal gene l(1)npr-1, cause initiation of expression of the 68C genes. A second series of experiments will precisely identify the cis-acting regulaoty nucleotides in and adjacent to the three genes by several different and complementary methods. Finally, the interaction of transacting regulatory molecules and the cis-acting regulatory sequences will be studied. While most of the proposed work will use Drosophila melanogaster genes, a detailed analysis of the structure and function of the homologous genes in several other related Drosophila species will also be undertaken. The result of the planned work will be a detailed knowledge of the molecular interactions that are involved in the hormonal and developmental regulation of the three structural genes of the 68C puff. These studies will contribute to the long-term objective of understanding the molecular mechanisms by which developmentally and hormonally regulated genes are controlled, and thus to the comprehension of differential gene expression, one of the fundamental processes in the development of multicellular organisms.